1. Field of the Invention
The present invention relates to a lens drive device, an image pickup device and a lens drive method, configured to control a lens barrel drive force, by detecting a posture and an operation of the image pickup device by use of an acceleration sensor and based on the detected information.
2. Description of the Related Art
In recent years, image pickup accuracy, rapidness, as well as low power consumption and drive stability have been further highly required of an image pickup device, such as a digital camera.
In order to satisfy these requirements, a built-in accelerometer is fitted into the image pickup device to detect a posture or a motion direction thereof with respect to a direction of gravity of the image pickup device and to perform various controls of the image pickup device based on information obtained by the accelerometer.
In order to photograph with high accuracy, one of the problems that remain to be solved is that an out of focus image is sometimes undesirably photographed depending on the posture of the image pickup device. Such a problem is caused by a still-position deviation of a lens existing in a lens drive unit, resulting from a looseness, such as a play or a backlash, thereby lacking sharpness in a photograph.
To deal with such a problem, it is proposed that an acceleration sensor be provided to detect the posture of the image pickup device via an output of the acceleration sensor. Corresponding to the detected posture of the image pickup device, the lens stationary position deviation is corrected, thereby allowing photography with high accuracy (For reference, see Japanese Application Publication Number Hei6-300962 and Japanese Application Publication Number 2005-265448).
Furthermore, in order to photograph rapidly, one of the problems that remain to be solved is that it is rather time-consuming to perform a focus adjustment; for example, when an automatic focusing is performed at the time of photographing, while moving the lens along the optical axis in order to determine a focus where an edge component of a photographed image reaches a peak. Since a range to perform focusing needs to be set wide, the focus adjustment becomes time-consuming.
To deal with such a problem, it is proposed that a subject position be predicted based on a posture of the image pickup device to narrow the range to perform focus adjustment, whereby rapid photographing can be expected to be realized (For reference, see Japanese Application Publication Number 2006-323121).
Meanwhile, concerning the image pickup device, a force (torque) necessary to drive a lens barrel varies with the posture of the image pickup device and a direction of the drive. For example, concerning the image pickup device having a collapsible lens barrel, when the lens barrel is placed in the gravity direction, namely downwards, the gravity promotes an extension of the lens barrel. In contrast, when the lens barrel is placed in the direction opposite to the gravity direction, namely upwards, the gravity facilitates a collapse or housing of the lens barrel.
Considering the above, on the one hand, to extend the lens barrel, when a photographing lens is placed upwards, a maximum torque is required because the gravity impedes the extension of the lens barrel. When the photographing lens is placed horizontally, a second largest torque is required. When the photographing lens is placed downwards, a minimum torque is required because the gravity facilitates the extension of the lens barrel with the gravity direction being consistent with the extension direction.
On the other hand, to house the lens barrel, when the photographing lens is placed downwards, a maximum torque is required because the gravity impedes the housing of the lens barrel. When the photographing lens is placed horizontally, a second largest torque is required. When the photographing lens is placed upwards, a minimum torque is required because the gravity facilitates the housing of the lens barrel with the gravity direction being consistent with the housing direction.
As illustrated heretofore, although the torque necessary to extend and house the lens barrel varies with the posture of the image pickup device, a conventional image pickup device always extends and houses the lens barrel with a constant drive torque.
More specifically, despite the fact that the maximum torque (a maximum extension torque will be used hereinafter) is required to extend the lens barrel when the photographing lens is placed upwards, the conventional image pickup device always extends the lens barrel unalterably with the maximum torque even when the photographing lens is placed in other postures. Likewise, despite the fact that the maximum torque (a maximum housing torque will be used hereinafter) is required to house the lens barrel when the photographing lens is placed downwards, the conventional image pickup device always houses the lens barrel unalterably with the maximum torque even when the photographing lens is placed in other postures.
The maximum extension torque and the maximum housing torque will be referred to as a maximum drive torque hereinafter. As illustrated heretofore, since the conventional image pickup device always drives the lens barrel unalterably with the maximum drive torque even when a smaller drive torque will do, a superfluous amount of electricity is consumed. Consequently, it is difficult for the image pickup device to meet the demand of energy-saving.
Moreover, concerning the conventional image pickup device, although a torque corresponding to the maximum drive torque required to extend and to house the lens barrel is set, the lens barrel has not been driven by a torque larger than the maximum drive torque. However, for example, in the cases wherein the image pickup device is operated in the middle of an intense movement or is forcibly taken out of a bag or a pocket, because an acceleration produced at the time operates, the lens barrel may not be able to be driven unless by the torque which is larger than the aforementioned maximum drive torque. In these cases, since neither the drive of the lens barrel is able to start nor the drive is able to be maintained, there is a problem with the conventional image pickup device in that a stable drive of the lens barrel cannot be realized.
In addition, there is also a collapsible lens barrel in which when in a non-photographing state, at least one group of lenses retreats sideways from a lens optical axis at the time of photographing and other lens groups are housed in an image pickup device body. Concerning such a collapsible lens barrel, when a power switch is turned on to photograph, if an acceleration larger than the prescribed value is applied to the image pickup device in the middle of moving the respective lens groups to photographing positions, occasionally the respective lens groups are not able to be moved to the photographing positions. The reason is that when the acceleration is applied to the lens groups, especially to the aforementioned lens group, which retreats sideways from the lens optical axis at the time of photographing, the torque becomes insufficient to move this lens group.